Warm congratulations to my friend @BarackObama. Look forward to continue to work together

David Cameron's tweet to President Barack Obama

When news broke in the early hours that he had won, Obama posted a photo of himself hugging First Lady Michelle with a message: “Four more years.”

That sparked an internet frenzy as the message set a new Guinness World Record for the most shared tweet ever.

More than 650,000 people around the world sent it on, nearly tripling the previous high set by pop megastar Justin Bieber, 18.

And the newly-elected two-term president broke more records when his victory made him the most popular person on Facebook ever with the most “likes” in 24 hours.

With 31million tweets flying around, they peaked at 327,452 per minute as the world toasted the news.

Republican rival Mitt Romney, 65, conceded defeat at 5am UK time and contacted Obama, America’s first black president, when he had secured enough votes in crucial swing states to seal a convincing win.

The President, 51, praised his supporters, from Hollywood stars to ordinary people, for making it all possible, telling them: “This happ-ened because of you, thank you. We’re all in this together. That’s how we campaigned and that’s who we are. Thank you.”

Huge celebrations erupted when he emerged on stage in his home town Chicago with Michelle, 48, and their daughters Sasha, 11, and Malia, 14, to deliver a victory speech to Stevie Wonder’s song, Signed, Sealed, Delivered, I’m Yours.

He said: “I return to the White House more determined than ever. We have picked ourselves up, we have fought our way back and we know in our hearts that for the United States of America the best is yet to come.

“I have never been more hopeful about America.”

David Cameron, 46, joined other world leaders who called him to congratulate as the president returned to Washington last night.

The PM tweeted: “Warm congratulations to my friend @BarackObama. Look forward to continue to work together.”

Obama promised to fix the US economy which is saddled with a monstrous £16trillion national debt.

And in a message of unity to the millions of Americans who did not back him, he said: “Our economy is recovering. A decade of war is ending. A long campaign is now over. And whether I earned your vote or not, I have listened to you, I have learned from you, and you’ve made me a better president.”

Obama praised wife Michelle and America for “falling in love with her”, saying: “I wouldn’t be the man I am today without the woman who agreed to marry me 20 years ago.”

Former President Bill Clinton, 66, was another supporter and bookies are making his Secretary of State wife Hillary, 65, the favourite to win the 2016 Presidential election.

Defeated Romney urged Democrats and Republicans to “put the people before the politics”, saying: “This is a time of great challenges for America, and I pray that the president will be successful in guiding our nation.”